摘要:

We describe the calculation of the spin‐wave spectrum for barium ferrite, a complex exchange‐coupled hexagonal ferrimagnetic compound, using a method first used in a similar calculation for yttrium iron garnet (YIG). The exchange integrals are calculated by fitting the Weiss molecular field approximation to the sublattice magnetizations while including single‐ion anisotropy. The value for the space‐averaged stiffness constant as calculated from the acoustic mode of the spin‐wave spectrum is 2.5×10−9Oe cm2, which compares favorably with values obtained by domain wall resonance, considering the accuracy of such measurements.

ISSN:0021-8979    

DOI:10.1063/1.345583

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Composites with 0‐3 connectivity were fabricated from barium titanate and phenolic resin powders. These composites were investigated for dielectric and piezoelectric properties with the active particle size. Under the condition of the same density and ceramic/polymer volume ratio, the dielectric constants and piezoelectric coefficients of composite increase as the ceramic particle size in composite increases. The surface layer model was used to explain these phenomena in our composite system and was confirmed experimentally. The thickness and dielectric constant of the surface layer of the powder prepared by grinding the sintered barium titanate ceramics were 1.59 &mgr;m and 105. When the ceramic particle size is larger than about 100 &mgr;m, the properties of the composite were nearly independent of size.

ISSN:0021-8979    

DOI:10.1063/1.345584

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The line shape of the intersubband optical absorption is calculated with the density‐functional formulation in a cylindrical quantum well. The resonance energy shifts due to the excitonlike effect and the depolarization effect are considered. Dynamical electric conductivity in this system is found to be of the similar form obtained by Ando [Z. Phys. B24, 33 (1976), and Phys. Rev. B13, 3468 (1976)] in a surface space‐charge layer.

ISSN:0021-8979    

DOI:10.1063/1.345585

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A quantum‐mechanical approach used to calculate the change of refractive index, &Dgr;n, due to free carriers in various doped silicon is presented. This approach uses a numerical Kramers–Kronig relation to analyze a calculated carrier‐related absorption spectrum below or near the energy‐band gap. The absorption spectrum is obtained by considering the optical transitions between energy bands and impurity bands, and the free‐carrier absorption due to acoustic phonons, optical phonons, and ionized impurities in a spherical nonparabolic band model. Values of &Dgr;nat wavelength &lgr;=1.3 and 1.6 &mgr;m for different doping levels are obtained. The results are applicable to both the integrated‐optics applications and optical‐probing applications in silicon.

ISSN:0021-8979    

DOI:10.1063/1.345586

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An actinide was successfully introduced into III‐V semiconductors and investigated with photoluminescence and secondary ion mass spectrometry (SIMS). The implanted uranium ion gives rise to relatively strong and sharp emissions between 1.60 to 1.69 &mgr;m in GaAs and at 1.67 &mgr;m in InP. The implantation was performed at an ion mean energy of 131 keV using a new type of high‐current metal ion source; the predicted depth profile of uranium was confirmed with SIMS. The emissions are a result of transitions between specific crystal‐field split spin‐orbit levels of possibly trivalent uranium (U3+) but most likely tetravalent uranium (U4+). The half‐width of the main 1601‐nm line in GaAs and the 1670‐nm line in InP is less than 0.46 meV at 6 K. Temperature‐dependent studies indicate that the emissions are associated with one center, and the luminescence is observed in GaAs and InP up to a temperature of 100 K after which it rapidly quenches.

ISSN:0021-8979    

DOI:10.1063/1.345587

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The optical properties of a novel system, the GaAs/GaP strained‐layer superlattice, are studied and compared with a theoretical model. Photoluminescence and photoreflectance measurements revealed that among the set of superlattices under study type‐I and type‐II behaviors (similar to those found in the lattice‐matched GaAs/AlAs system) are present. The evolution of the photoluminescence peaks as a function of temperature and excitation density supported the assignment of the transitions involved. This is to our knowledge the first observation of direct (type‐I) and indirect (type‐II) transitions in strained‐layer superlattices. A comparison with a theoretical model has led to an estimation of the conduction‐band offset as 0.4 eV, which is the first value obtained from experiment in a GaAs/GaP heterojunction.

ISSN:0021-8979    

DOI:10.1063/1.345588

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polyimide films deposited on fused quartz, silicon, and ceramic substrates are examined. Waveguide techniques are used to determine the guide modes from which the index of refraction is inferred. Film thicknesses are determined from transmission interferences and, independently, from a luminescence‐induced reflection interference pattern. Using a waveguide configuration we also observed and analyzed Raman scattering features in the region above 1000 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.345589

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A multiparameter, nonlinear‐curve fitting method is used to determine the refractive indices, absorption coefficients, and thicknesses of mixed yttria‐silica films from transmittance spectra. Both homogeneous and inhomogeneous models of refractive index in the films are used for the data analysis. Results suggest that inhomogeneity in the films should be considered when investigating the optical properties of thin films. However, care must be taken when computing a refractive index gradient in an absorbing film as both absorption and index gradients can affect the optical transmittance in a similar manner.

ISSN:0021-8979    

DOI:10.1063/1.345590

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It is shown that the blue luminescence band appearing at room temperature in ZnSe is seen in metalorganic chemical vapor deposition (MOCVD) epilayers with carrier concentration 1×1018cm−3. The photon energy at the emission peak is the same in this material as in material with much lower carrier concentration. Properties of the blue band are surveyed to discriminate between different possible assignments. It is concluded that Shirakawa and Kukimoto [J. Appl. Phys.51, 2014 (1980)] were correct in assigning it to a transition between a free hole and an electron bound to a donor. However, not all donors contribute. There is a cutoff energy within the spread of donor levels above which there is negligible contribution to the emission. It is suggested that the cutoff corresponds to a localization edge of the same nature as the mobility edge.

ISSN:0021-8979    

DOI:10.1063/1.345591

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

X-ray photoelectron spectroscopy (XPS) was used to investigate potassium-assisted, facile oxidation of silicon nitride (Si3N4) thin films on Si(100) substrates. The nitride films, 0.8–2.5 nm thick, were grown by heating the Si(100) crystal in hydrazine. Potassium (K) deposited onto the Si3N4surface at room temperature in a background of oxygen resulted in the formation of potassium peroxide (K2O2) overlayers. Annealing the sample at 975 K for only 60 s decomposed the K2O2overlayer, desorbed K from the surface, and efficiently oxidized the underlying substrate. The XPS Si(2p) spectra indicate formation of silicon oxynitride on the surface. In the early stages of oxidation, up to 100% of the oxygen originally deposited as K2O2, was converted to silicon oxynitride after annealing. The enhanced oxidation rate under these conditions, relative to direct thermal oxidation, is attributed to the large concentration of reactive oxygen on the surface when the K2O2thermally decomposes.

ISSN:0021-8979    

DOI:10.1063/1.345594

出版商:AIP    

年代:1990

数据来源: AIP